U.S. patent number 7,272,926 [Application Number 11/142,291] was granted by the patent office on 2007-09-25 for exhaust emission control device for internal combustion engine.
This patent grant is currently assigned to Denso Corporation. Invention is credited to Yuji Kosaka.
United States Patent |
7,272,926 |
Kosaka |
September 25, 2007 |
Exhaust emission control device for internal combustion engine
Abstract
A DPF is used in an internal combustion engine for trapping PM
discharged from an engine body. Presence and absence of an
abnormality in the DPF is evaluated using differential pressure,
which is between the front and the rear of the DPF. The
differential pressure considerably decreases or considerably
increases due to breakage or plugging of the DPF in an exhaust
emission control device. The abnormality in the DPF is evaluated
when a large deviation arises between a PM amount calculated in
accordance with differential pressure, which is between the front
and the rear of the DPF, and a PM amount calculated through
integration of a PM discharge amount measured in accordance with an
engine operating state. Thereby, presence and absence of the
abnormality such as plugging and breakage in the DPF can be
correctly detected.
Inventors: |
Kosaka; Yuji (Obu,
JP) |
Assignee: |
Denso Corporation (Kariya,
JP)
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Family
ID: |
34937186 |
Appl.
No.: |
11/142,291 |
Filed: |
June 2, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050268597 A1 |
Dec 8, 2005 |
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Foreign Application Priority Data
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Jun 3, 2004 [JP] |
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2004-165694 |
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Current U.S.
Class: |
60/295; 60/311;
60/297; 60/277 |
Current CPC
Class: |
F01N
3/023 (20130101); F01N 11/002 (20130101); F01N
9/005 (20130101); F01N 9/002 (20130101); F02D
41/1448 (20130101); Y02T 10/40 (20130101); F01N
2560/14 (20130101); F02D 2041/1433 (20130101); F01N
2560/06 (20130101); F01N 2550/04 (20130101); F01N
2560/08 (20130101); F02D 2200/0812 (20130101); Y02T
10/47 (20130101) |
Current International
Class: |
F01N
3/00 (20060101); F01N 3/02 (20060101) |
Field of
Search: |
;60/277,297,311,295 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1180210 |
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Feb 2002 |
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EP |
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H07-317529 |
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May 1994 |
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JP |
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WO 01/27447 |
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Apr 2001 |
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WO |
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WO 2004/016916 |
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Feb 2004 |
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WO |
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Other References
Patent Abstracts of Japan, vol. 1996, No. 04, Apr. 30, 1996, &
JP 07 317529 A, Dec. 5, 1995. cited by other.
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Primary Examiner: Denion; Thomas
Assistant Examiner: Edwards; Loren
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Claims
What is claimed is:
1. An exhaust emission control device for an internal combustion
engine, the exhaust emission control device comprising: a
particulate filter that traps exhaust particulates contained in
exhaust gas discharged from an internal combustion engine body; and
a sediment amount calculation means that calculates a sediment
amount of exhaust particulates, which are trapped and accumulated
by the particulate filter, for evaluating necessity of regeneration
of the particulate filter in accordance with the sediment amount,
wherein the sediment amount calculation means includes a first
sediment calculation means and a second sediment amount calculation
means, the first sediment calculation means calculates a first
sediment amount in accordance with differential pressure between a
front side of the particulate filter and a rear side of the
particulate filter, and the second sediment amount calculation
means calculates an amount of exhaust particulates discharged from
the internal combustion engine body per unit of time in accordance
with an operating state of the internal combustion engine body, the
second sediment amount calculation means integrating the amount of
exhaust particulates to calculate a second sediment amount, the
exhaust emission control device further comprising: an abnormality
evaluating means that evaluates presence and absence of an
abnormality in flow of exhaust gas, which flows through the
particulate filter, in accordance with a correspondence between the
first sediment amount and the second sediment amount; a selection
means that selects from the first sediment calculation means and
the second sediment calculation means in accordance with the
operating state of the internal combustion engine body for
evaluating necessity of regeneration of the particulate filter,
wherein the second sediment amount calculation means calculates the
second sediment amount by integrating the amount of exhaust
particulates, which are discharged from the internal combustion
engine body, with the first sediment amount, which is calculated
immediately before the sediment amount calculation means is
switched from the first sediment calculation means, the abnormality
evaluating means expresses the correspondence between the first
sediment amount and the second sediment amount using a difference
between the sediment amount calculated immediately before
switchover, which is from the second sediment amount calculation
means to the first sediment calculation means, and the sediment
amount calculated immediately after the switchover from the second
sediment amount calculation means to the first sediment calculation
means, and when the difference between the first sediment amount
and the second sediment amount is out of a predetermined reference
range, the abnormality evaluating means determines the
correspondence is not coordinated, and the abnormality evaluating
means determines the particulate filter to be abnormal.
2. The exhaust emission control device according to claim 1,
further comprising: a difference distribution calculation means
that stores a frequency of occurrence for each value of the
difference between the first sediment amount and the second
sediment amount in a predetermined time period, wherein the
difference distribution calculation means calculates an upper
representative value and a lower representative value, which are
representative of a distribution of the differences in the
predetermined time period, in accordance with the frequency of
occurrence, which is stored by the difference distribution
calculation means, and the abnormality evaluating means sets a
range of the difference, which is represented by the upper
representative value and the lower representative value, as the
predetermined reference range.
3. The exhaust emission control device according to claim 1,
wherein the operating state of the internal combustion engine body
includes engine speed and an accelerator position.
4. The exhaust emission control device according to claim 1,
wherein the abnormality is breakage in the particulate filter.
5. The exhaust emission control device according to claim 1,
wherein the abnormality is plugging in the particulate filter.
6. A method of controlling exhaust emission for an internal
combustion engine, the method comprising: trapping, in a
particulate filter, exhaust particulates contained in exhaust gas
discharged from an internal combustion engine body; and calculating
a sediment amount of exhaust particulates, which are trapped and
accumulated by the particulate filter, and evaluating necessity of
regeneration of the particulate filter in accordance with the
sediment amount, said calculating comprising: calculating a first
sediment amount in accordance with differential pressure between a
front side of the particulate filter and a rear side of the
particulate filter; and calculating an amount of exhaust
particulates discharged from the internal combustion engine body
per unit of time in accordance with an operating state of the
internal combustion engine body, and integrating the amount of
exhaust particulates to calculate a second sediment amount; and
evaluating a presence or absence of an abnormality in flow of
exhaust gas, which flows through the particulate filter, in
accordance with a correspondence between the first sediment amount
and the second sediment amount; wherein said evaluating a presence
or absence of an abnormality in flow of the exhaust gas in
accordance with a correspondence between the first sediment amount
and the second sediment amount includes: calculating a difference
between the first sediment amount and the second sediment amount;
and determining the particulate filter to be abnormal if the
difference between the first sediment amount and the second
sediment amount is out of a predetermined reference range.
7. The method according to claim 6, further comprising: storing a
frequency of occurrence for each value of the difference between
the first sediment amount and the second sediment amount in a
predetermined time period; calculating an upper representative
value and a lower representative value, which are representative of
a distribution of the differences in the predetermined time period,
in accordance with the stored frequency of occurrence; and setting
a range of the difference, which is represented by the upper
representative value and the lower representative value, as the
predetermined reference range.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on and incorporates herein by reference
Japanese Patent Application No. 2004-165694 filed on Jun. 3,
2004.
FIELD OF THE INVENTION
The present invention relates to an exhaust emission control device
for an internal combustion engine, to which a particulate filter is
provided. More particularly, the present invention relates to
regeneration of a particulate filter.
BACKGROUND OF THE INVENTION
A diesel type internal combustion engine involves a problem in
exhaust particulates (particulate matters, PM) contained in exhaust
gas discharged from an internal combustion engine body.
Accordingly, a diesel particulate filter (DPF) is used to trap PM.
PM are trapped and accumulated in the DPF, and the PM are
periodically burned and removed, so that the DPF is regenerated and
the PM trapping capacity of the DPF is restored. Regeneration of
the DPF can be made in operation of the internal combustion engine.
For instance, the oxidation action of the oxidation catalyst such
as platinum is used. The oxidation catalyst is increased in
temperature by post injection or retard in ignition timing, so that
regeneration of a DPF is started.
Delay in timing of regeneration of the DPF causes fast burn, and
advance in the timing of regeneration of the DPF may increase fuel
consumption. Accordingly, necessity of regeneration of the DPF is
evaluated in accordance with a PM sediment amount (PM amount),
which is measured. As the PM amount increases, differential
pressure between the front of the DPF and the rear of the DPF
increases. Therefore, the PM amount may be calculated in accordance
with the differential pressure of the DPF. However, the calculation
of the PM amount, which is based on the differential pressure of
the DPF, is not necessarily satisfactory in accuracy of measurement
in an unsteady operating state. The unsteady operating state
includes a state, in which exhaust gas flows through the DPF at a
small flow rate, and a transient state. According to JP-A-7-317529
and U.S. Pat. No. 6,758,039 (JP-A-2004-019529), the PM discharge
amount is calculated in accordance with an operating state of the
internal combustion engine, so that the PM discharge amount is
integrated for calculating the PM amount.
Here, when abnormality is caused in flow of exhaust gas due to
plugging or breakage in the DPF, the differential pressure of the
DPF changes from that in a normal condition, in which exhaust gas
normally flows. The abnormality in the DPF can be detected in
accordance with the differential pressure. Specifically, when the
differential pressure of the DPF is less than a predetermined
value, exhaust gas is determined to be leaking due to breakage of
the DPF.
When the PM amount is large, abnormality in the DPF can be
satisfactory detected, since the differential pressure of the DPF
sufficiently changes at the time of breakage. However, when the PM
amount is small as immediately after completion of regeneration of
the DPF, the differential pressure does not sufficiently change.
Accordingly, presence and absence of the abnormality in the DPF may
not be correctly detected.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the present
invention to provide an exhaust emission control device for an
internal combustion engine, the exhaust emission control device
being capable of detecting states of breakage and plugging of a DPF
with high accuracy.
According to the present invention, an exhaust emission control
device for an internal combustion engine includes a particulate
filter and a sediment amount calculation means. The particulate
filter traps exhaust particulates contained in exhaust gas
discharged from an internal combustion engine body. The sediment
amount calculation means calculates a sediment amount of exhaust
particulates, which are trapped and accumulated by the particulate
filter, for evaluating necessity of regeneration of the particulate
filter in accordance with the sediment amount. The sediment amount
calculation means includes a first sediment calculation means and a
second sediment amount calculation means. The first sediment
calculation means calculates a first sediment amount in accordance
with differential pressure between the front side of the
particulate filter and the rear side of the particulate filter. The
second sediment amount calculation means calculates an amount of
exhaust particulates discharged from the internal combustion engine
body per unit of time, in accordance with an operating state of the
internal combustion engine body. The second sediment amount
calculation means integrates the amount of exhaust particulates to
calculate a second sediment amount. The exhaust emission control
device further includes an abnormality evaluating means. The
abnormality evaluating means evaluates presence and absence of an
abnormality in flow of exhaust gas, which flows through the
particulate filter, in accordance with a correspondence between the
first sediment amount and the second sediment amount.
The exhaust emission control device further includes a selection
means. The selection means selects from the first sediment
calculation means and the second sediment calculation means in
accordance with the operating state of the internal combustion
engine body for evaluating necessity of regeneration of the
particulate filter. The second sediment amount calculation means
calculates the second sediment amount by integrating the amount of
exhaust particulates, which are discharged from the internal
combustion engine body, with the first sediment amount, which is
calculated immediately before the sediment amount calculation means
is switched from the first sediment calculation means. The
abnormality evaluating means expresses the correspondence between
the first sediment amount and the second sediment amount using a
difference between the sediment amount calculated immediately
before switchover, which is from the second sediment amount
calculation means to the first sediment calculation means, and the
sediment amount calculated immediately after the switchover from
the second sediment amount calculation means to the first sediment
calculation means. When the difference between the first sediment
amount and the second sediment amount is out of a predetermined
reference range, the abnormality evaluating means evaluates the
correspondence is not coordinated, and the abnormality evaluating
means determines the particulate filter to be abnormal.
The exhaust emission control device further includes a difference
distribution calculation means. The difference distribution
calculation means stores a frequency of occurrence for each value
of the difference between the first sediment amount and the second
sediment amount in a predetermined time period. The difference
distribution calculation means calculates an upper representative
value and a lower representative value, which are representative of
a distribution of the differences in the predetermined time period,
in accordance with the frequency of occurrence, which is stored by
the difference distribution calculation means. The abnormality
evaluating means sets a range of the difference, which is
represented by the upper representative value and the lower
representative value, as the predetermined reference range.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present
invention will become more apparent from the following detailed
description made with reference to the accompanying drawings. In
the drawings:
FIG. 1 is a schematic view showing an internal combustion engine
provided with an exhaust emission control device according to an
embodiment of the present invention;
FIG. 2 is a flowchart showing a control routine executed in the
exhaust emission control device for calculating a sediment amount
of exhaust particulates, according to the embodiment;
FIG. 3 is a flowchart showing a routine for evaluation of a
particulate filter, according to the embodiment;
FIG. 4 is a graph showing a relationship between a deviation, which
is between sediment amounts of exhaust particulates calculated
using different methods, and a frequency of occurrence of the
deviation;
FIG. 5A is a first graph showing changes in a calculated value of
the sediment amount of exhaust particulates as time elapses in a
normal condition, FIG. 5B is a second graph showing changes in a
calculated value of the sediment amount of exhaust particulates as
time elapses when the particulate filter is plugged, and FIG. 5C is
a third graph showing changes in a calculated value of the sediment
amount of exhaust particulates as time elapses when the particulate
filter is broken;
FIG. 6 is a graph showing a relationship between the sediment
amount of exhaust particulates and differential pressure between
the front and the rear of the particulate filter; and
FIG. 7 is a flowchart showing a routine for evaluation of a
particulate filter, according to a modification of the embodiment
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Embodiment
As shown in FIG. 1, a diesel particulate filter (DPF) 4 is mounted
to an exhaust passage 3, which communicates with an exhaust port of
an engine body 1. The DPF 4 includes a base body, which is formed
by molding a heat resisting ceramics, such as cordierite into a
honeycomb construction, for example. The honeycomb construction has
a number of cells, which form flow passages of exhaust gas. The
cells are sealed such that the inlet sides the outlet sides thereof
are made alternate, and coated with an oxidation catalyst such as
Pt over the cell wall surfaces. Exhaust gas discharged from the
engine body 1 flows downstream while flowing through porous
partitions of the DPF 4, and PM is trapped in the meantime to be
gradually accumulated.
Exhaust temperature sensors 52a, 52b are provided in the exhaust
passage 3 to detect exhaust temperature of exhaust gas.
Differential pressure sensor 53 is provided to detect differential
pressure between the front and the rear of the DPF 4 in order to
measure an amount of PM, which are trapped by the DPF 4 and
accumulated. The differential pressure sensor 53 is interposed
between a pressure introduction pipe 31a, which is communicated
with the exhaust passage 3 on the upstream side of the DPF 4, and a
pressure introduction pipe 31b, which is communicated to the
exhaust passage 3 on the downstream side of the DPF 4. The
differential pressure sensor 53 outputs a signal corresponding to
differential pressure (DPF front and rear differential pressure,
DPF differential pressure) between the front and the rear of the
DPF 4, i.e., between the upstream and the downstream of the DPF 4.
Temperature sensors 52a, 52b are provided immediately upstream and
downstream of the DPF 4 to detect temperature of exhaust gas
flowing through the DPF 4. Besides, an airflow meter 54 is mounted
to an intake passage 2 to detect an amount of intake air.
An ECU (engine control unit, control means) 51 inputs thereinto
output signals of the various sensors 51 to 54 and the like to
detect states of respective components.
FIG. 2 shows a control routine implemented by a microcomputer that
constructs the ECU 51. The control routine is implemented at a
predetermined control interval by timer interruption in the ECU 51.
In STEP S101, various input signals such as DPF differential
pressure, exhaust temperature, and an intake amount are read. In
STEP S102, which serves as a selection means, it is evaluated
whether a PM sediment amount calculation based on DPF differential
pressure (PM calculation with DPF dp) is in an authorized state.
When an engine operating state is a steady operation, the PM
calculation with DPF dp is evaluated to be in the authorized state.
The steady operation is evaluated in accordance with engine speed
and an accelerator position. When a positive determination is given
in STEP S102, the procedure proceeds to STEP S103, and when a
negative determination is given in STEP S102, the procedure
proceeds to STEP S104.
In STEP S103, which serves as a first sediment amount calculation
means (first sediment calculation means) is implemented to
calculate a PM sediment amount (PM amount) in accordance with the
DPF differential pressure. Here, the first sediment calculation
means calculates a first sediment amount in accordance with the DPF
differential pressure. The calculation of the PM amount is carried
out in accordance with DPF differential pressure, the intake
amount, and exhaust temperature. The calculation of the PM amount
is carried out by converting an amount of intake air, which is
obtained as a mass flow rate, into a volumetric flow rate, for
example. The volumetric flow rate is corrected in accordance with
exhaust temperature to be a flow rate of exhaust gas flowing
through the DPF 4, based on an assumption, in which an intake air
is discharged from the engine body 1 as it is. A PM amount is
obtained according to a data map in accordance with a flow rate of
exhaust gas and DPF differential pressure. Thereafter, the
procedure shifts to return.
Following STEPS S104, S105 serve as a second sediment amount
calculation means (second sediment calculation means). In STEP
S104, the PM amount, which is discharged from the engine, is
calculated in accordance with an engine operating state (engine
state). Here, the second sediment calculation means calculates a
second sediment amount in accordance with the engine state. The PM
amount is a discharge amount, which is measured in units of control
periods of the present flows. The PM discharge amount is calculated
by multiplying the amount of intake air by a predetermined
coefficient, for example. The coefficient is in proportion to a PM
concentration in exhaust gas. High accuracy is preferably achieved
by beforehand obtaining a data map, to which the coefficient
corresponds in accordance with an engine state, by conducting
experiments or the like. In subsequent STEP S105, the PM discharge
amount calculated in STEP S104 is added to the PM amount at the
previous time to calculate the PM amount at the present time. After
STEP S105 is implemented, the procedure shifts to return. STEP S103
is a calculation method of the PM amount different from the
calculation method in STEP S104 and STEP S105. The PM amount at the
previous time is needed in calculation in STEP S104 and STEP S105.
Therefore, the PM amount obtained in STEP S103 or STEP S105 is
stored and updated as the PM amount at the previous time.
According to the above processing, when the engine is in a steady
operating state (normal state), the PM amount is calculated in
accordance with DPF differential pressure at the present time. When
the engine is in an unsteady operating state, the PM amount is
obtained by adding an integrated PM discharge amount to the PM
amount, which is calculated in accordance with DPF differential
pressure at the previous time immediately before the engine state
is switched over from the steady operating state to the unsteady
operating state. Here, the integrated PM discharge amount is an
amount accumulated after the engine becomes in an unsteady
operating state.
The calculation of the PM amount in STEP S103 is referred to as the
PM calculation with DPF dp. The calculation of the PM amount in
STEP S104 and STEP S105 is referred to as a PM calculation with
engine state. The PM calculation with DPF dp is fundamentally
higher in accuracy than the PM calculation with engine state. The
two kinds of calculation methods are switched over to each other.
In an unsteady operating state such as the transient state, the PM
calculation with engine state is higher in accuracy than the PM
calculation with DPF dp. Accuracy of the PM calculation with engine
state and accuracy of the PM calculation with DPF dp are beforehand
experimentally clarified, so that the criterion, which is for
evaluating whether the engine is presently in the steady operating
state, is obtained. The engine state, in which PM calculation with
DPF dp is higher in accuracy than the PM calculation with engine
state, is evaluated to be the steady operating state.
Subsequently, an evaluation of the DPF 4 and a failsafe control for
abnormality of the DPF 4 will be described with reference to FIG.
3. STEPs S201 to S204 serve as a difference distribution
calculation means. In STEP S201, switchover, which is from the PM
calculation with engine state to the PM calculation with DPF dp, is
used as a trigger for calculation of a PM amount deviation. When
the switchover is detected, the PM amount deviation is calculated.
The switchover, which is from the PM calculation with engine state
to the PM calculation with DPF dp, is detected in accordance with
results in STEP S102 (positive, negative) in the following manner.
When a negative determination is given in STEP S102, that is, when
the PM calculation with DPF dp is not determined to be in the
authorized state, a predetermined flag is set. By contrast, when a
positive determination is given in STEP S102, that is, when the PM
calculation with DPF dp is determined to be in the authorized
state, it is evaluated whether the flag has been set. When the flag
has been set, the PM calculation with engine state has been
previously set. That is, when the flag has been set, it is
determined that the switchover, which is from the PM calculation
with engine state to the PM calculation with DPF dp, has been
made.
Next, a calculation of the PM amount deviation is described. The PM
amount deviation is a deviation between the PM amount immediately
before the switchover, which is from the PM calculation with engine
state to the PM calculation with DPF dp, and the PM amount
immediately after the switchover. Here, the PM amount deviation
corresponds to a value obtained by subtracting the PM calculation
with engine state from the PM calculation with DPF dp.
In STEP S202, a frequency of occurrence corresponding to the PM
amount deviation is stored in a memory. That is, a region of the
memory, in which the frequency of occurrence is stored
corresponding to a value of the PM amount deviation, is allotted.
Subsequently, the frequency of occurrence of the PM amount
deviation at this time is increased by 1.
Specifically, distribution of the PM amount deviation is shown by
the graph in FIG. 4, and when a specific PM amount deviation is
frequently obtained, the occurrence of the specific PM amount
deviation becomes high, and a distribution of the PM amount
deviation is biased around the specific PM amount deviation.
For the purpose of economizing a memory capacity, the values of the
PM amount deviation may be divided into several segments. In this
case, a region of a memory may be set to be corresponding to each
segment of the PM amount deviation in a one-to-one
relationship.
In STEP S203, it is evaluated whether a travel distance obtained
from a trip meter exceeds a threshold. When a negative
determination is given, the processings in STEP S201 and the
following STEPs are repeated. Accordingly, until the travel
distance reaches the threshold, the PM amount deviation is
calculated and the frequency of occurrence is updated. When the
travel distance reaches the threshold, a histogram is created. The
histogram shows the PM amount deviation in a predetermined time
period until the travel distance reaches the threshold. The
histogram indicates a distribution of the PM amount deviation as
shown in FIG. 4.
When a positive determination is given in STEP S203, that is, when
the travel distance reaches the threshold, the histogram is fixed,
i.e., is determined as the PM amount deviation occurrence reference
property (PM deviation occurrence reference) in STEP S204. The
maximum and minimum values of the distribution of the PM amount
deviation are calculated as a representative value that prescribes
the reference property. Here, the maximum and minimum values, which
are respectively upper and lower representative values of the
distribution of the PM amount deviation, are represented by an
average value and a standard deviation, for example. For example,
the maximum value of the distribution of the PM is represented by
the average value+2.times.standard deviation, and the minimum value
of the distribution of the PM is represented by the average
value-2.times.standard deviation. Alternatively, the PM amount
deviation may be simply compared with the maximum and minimum
values in STEP S205, so that the maximum and minimum values may be
updated. Subsequently, the maximum and minimum values, which are at
the time point when the travel distance reaches the threshold, may
be set as the upper and lower representative values of the
distribution of the PM amount deviation.
In STEP S205, the switchover, which is from the PM calculation with
engine state to the PM calculation with DPF dp, is used as the
trigger in the same manner as in STEP S201, and when the switchover
is performed, the PM amount deviation is calculated.
In STEP S206, it is evaluated how the PM amount deviation obtained
in STEP S205 is positioned relative to the reference property,
i.e., the PM deviation occurrence reference shown by the histogram.
Besides, it is evaluated in STEP S206 whether the PM amount
deviation obtained in STEP S205 is equal to or greater than the
maximum value of the reference property. When a negative
determination is given, it is evaluated in STEP S209 whether the PM
amount deviation is equal to or less than the minimum value of the
reference property. When a negative determination is given in STEP
S209, that is, when the PM amount deviation is within a reference
range that corresponds to a range from the minimum value to the
maximum value of the reference property, it is determined that the
DPF 4 is not abnormal, and the processings in STEP S205 and the
following STEPs are repeated.
When a positive determination is given in STEP S206, that is, the
PM amount deviation is determined to be equal to or greater than
the maximum value of the reference property, the routine proceeds
to STEP S207. It is evaluated in STEP S207 whether the PM amount
deviation becomes equal to or greater than the maximum value of the
reference property successively for n times. That is, when a
positive determination is given in STEP S206, a variable is
incremented 1 by 1. This variable counts the number of the
conditions, in which the PM amount deviation becomes equal to or
greater than the maximum value of the reference property. When a
negative determination is given in STEP S206, the variable is
reset.
When a negative determination is given in STEP S207, that is, the
PM amount deviation is not determined to be equal to or greater
than the maximum value of the reference property successively for n
times, the processings in STEP S205 and the following STEPs are
repeated.
When a positive determination is given in STEP S207, it is
evaluated in STEP S208 that the DPF is plugged. Subsequent to STEP
S208, a failsafe measure such as lighting of an alarm lamp is taken
in STEP S212.
By contrast, when a positive determination is given in STEP S209,
that is, the PM amount deviation is determined to be equal to or
less than the minimum value of the reference property, the routine
proceeds to STEP S210. It is evaluated in STEP S210 whether the PM
amount deviation becomes equal to or less than the minimum value of
the reference property successively for n times.
That is, when a positive determination is given in STEP S209, a
variable is incremented 1 by 1. This variable counts the number of
the conditions, in which the PM amount deviation becomes equal to
or less than the minimum value of the reference property. The
variable is reset when a positive determination is given in STEP
S206, or when a negative determination is given in STEP S209. When
a negative determination is given in STEP S210, the processings in
STEP S205 and the following STEPs are repeated.
When a positive determination is given in STEP S210, the routine
proceeds to STEP S211, in which it is determined that the DPF is
broken. Subsequently, the procedure proceeds to STEP S212, in which
a failsafe measure is taken.
In the exhaust emission control device, abnormality of the DPF 4 is
detected. In FIGS. 5A, 5B, 5C, the unsteady operating state changes
to the steady operating state in the portions shown by circles.
That is, the PM calculation with engine state is switched to the PM
calculation with DPF dp in the portions shown by the circles.
An actual value of the PM amount is considered to be substantially
the same immediately before and immediately after the switchover,
which is from the PM calculation with engine state to the PM
calculation with DPF dp. Therefore, when the DPF 4 is neither
plugged nor broken, the PM amount calculated using the PM
calculation with DPF dp is not largely different from the PM amount
calculated using the PM calculation with engine state. Therefore,
the PM amount deviation, which is the difference between the PM
amount calculated using the PM calculation with engine state and
the PM amount calculated using the PM calculation with DPF dp, is
distributed centering substantially on 0.
That is, the PM amount, which is calculated using the PM
calculation with DPF dp, is affected by plugging or breakage of the
DPF 4. However, the PM amount, which is calculated using the PM
calculation with engine state, is not affected by plugging,
breakage of the DPF 4 or the like. Accordingly, presence and
absence of abnormality in the DPF 4 such as plugging and breakage
can be evaluated based on a correspondence between the PM amounts,
which are calculated using the PM calculation with DPF dp and the
PM calculation with engine state. Besides, the PM amount, which is
calculated through integration of a discharge amount of exhaust
particulates and is compared with the PM amount calculated using
the PM calculation with DPF dp, substantially corresponds to the PM
amount at this time point. That is, the PM amount, which is
calculated using the PM calculation with engine state,
substantially corresponds to the actual PM amount even when
immediately after completing regeneration of the DPF 4, in which
the PM amount is small, or even when the DPF 4 is still plugged or
broken. Therefore, presence and absence of abnormality in the DPF 4
is not hard to be evaluated even in a time period shortly after
completing regeneration, in which the PM amount is small.
In contrast, when the DPF 4 is plugged or broken, it results as
follows. As shown in FIG. 6, when the DPF 4 is plugged, flow
resistance increases in the DPF 4, and differential pressure of the
DPF 4 increases as compared with differential pressure of the DPF 4
in the normal condition. Therefore, as referred to FIG. 4, a center
of the distribution of the PM amount deviation shifts to the +
side. Besides, the probability that the PM amount deviation becomes
equal to or greater than the maximum value of the reference
property, i.e., the PM deviation occurrence reference shown by the
histogram becomes high.
By contrast, as referred to FIG. 4, when the DPF 4 is broken,
differential pressure of the DPF 4 decreases as compared with the
differential pressure of the DPF 4 in the normal condition, due to
leakage of exhaust gas from a broken portion of the DPF 4.
Therefore, a center of the distribution of the PM amount deviation
shifts to the - side. Accordingly, the probability that the PM
amount deviation becomes equal to or less than the minimum value of
the reference property becomes high.
Accordingly, an abnormality in the DPF 4 can be correctly evaluated
using the above control routine.
Besides, an actual value of the PM amount is substantially the same
immediately before and immediately after the switchover, which is
from the PM calculation with engine state to the PM calculation
with DPF dp. In this situation, the difference, which is between
the PM calculation with engine state and the PM calculation with
DPF dp, is calculated to evaluate abnormality in the DPF 4.
Thereby, abnormality in the DPF 4 need not to be evaluated in both
the methods at all times to obtain the PM amount, so that an
excessive load can be eliminated in calculation.
Here, for the purpose of evaluation of abnormality in the DPF 4,
the PM amount may be calculated in both the methods at all times,
and presence and absence of abnormality in the DPF 4 may be
evaluated each time.
Besides, the integrated value of the PM discharge amount is added
to the PM amount, which is calculated using the PM calculation with
DPF dp at the previous time, so that the PM amount in the unsteady
operating state is calculated. Thereby, an error, which involves a
relatively large error, caused in the PM calculation with engine
state is not cumulated over a long period.
The PM amount, which is integrated using the PM calculation with
engine, is relatively large in error relative to the actual PM
amount. Here, a time period, in which the PM amount is integrated
using the PM calculation with engine is limited to a period of
time, in which the PM amount is not calculated using the PM
calculation with DPF dp. Thereby, a load in calculation does not
become excessive in spite of using two kinds of the PM amount
calculation means. Furthermore, accumulation of errors in the PM
calculation with engine, which is relatively large in error, can be
restricted over a long term.
In addition, the reference property, which is for evaluation of
presence and absence of abnormality in the DPF 4, is learned in the
operation of the engine. Thereby, changes, which are due to aging,
and individual variations can be absorbed. Here, simply, such
changes and individual differences may be beforehand stored as
fixed values.
(Modification)
As described above, the number of times, in which the positive
determinations are successively given in STEP S206, is counted, in
order to enhance the accuracy in evaluation. Besides, the number of
times, in which the negative determinations are successively given
in STEP S206 and the positive determinations are given in STEP
S209, is counted. Thereby, whether occurrence is successive for n
times is evaluated in STEPs S207, S210. However, the accuracy in
evaluation can be enhanced in another way.
As shown in FIG. 7, it is evaluated in STEP S2071 whether the
frequency of occurrence, in which the PM amount deviation is equal
to or greater than the maximum value of the reference property, is
equal to or greater than a predetermined value m %. Besides, it is
evaluated in STEP S2101 whether the frequency of occurrence, in
which the PM amount deviation is equal to or less than the minimum
value of the reference property, is equal to or greater than a
predetermined value m %. The frequency of occurrences is
represented in a rate to the number of times, in which the
switchover, which is from PM calculation with engine state to PM
calculation with DPF dp, is made.
Therefore, the frequency of occurrence is calculated by counting
the number of times, in which positive determinations are given in
STEP S206, together with counting the number of times, in which the
switchover, which is from PM calculation with engine state to PM
calculation with DPF dp, is made. Besides, the frequency of
occurrence is calculated by counting the number of times, in which
negative determinations are given in STEP S206 and positive
determinations are given in STEP S209, together with counting the
number of times, in which the switchover is made.
Thus, as described above, the reference range for evaluation of
presence and absence of abnormality in the DPF 4 is learned while
the engine is operated, so that an erroneous evaluation of presence
and absence of the abnormality in the particulate filter may be
restricted.
Various modifications and alternations may be diversely made to the
above embodiments without departing from the spirit of the present
invention.
* * * * *